High efficiency fuel injection system for gas appliances

ABSTRACT

A unique control system is provided for optimizing and effecting efficient combustion of gas appliances by controlling the proportion of fuel and air variables. The control system provides continuous active feedback of the combustion event by detecting the level of exhaust gases such as CO 2  to trigger the modulation of a gas valve. Based upon the detected level, a control signal is generated by the system and received by a processor to adjust pressure and gas flow for future combustion events. Accordingly, the control system varies the proportion of air to fuel inflow to a prescribed optimum range thereby achieving efficient fuel combustion.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of my prior U.S. applicationSer. No. 11/080,830, filed Mar. 14, 2005.

BACKGROUND OF THE INVENTION

The present invention relates to an improved method and apparatus forimproving the efficiency of gas appliances.

Gas appliances such as water heaters, floor heaters, space heaters, roomheaters, boilers, central furnaces, clothes dryers and cooking ranges,have gained wide acceptance with the consuming public. Conventional gasheating appliances typically employ manually operated gas valves toregulate and control gas flow to burners for combustion to generate heatfrom the burning of natural or propane gas.

The fixed orifice in a conventional gas valve, however, is not capableof continuous active adjustment of pressure and flow rate of gas intothe burner resulting in inefficient combustion, i.e., too little heatand too much exhaust generated from a gas-heating appliance.

Excessive gas flow with inadequate air in the combustion mixture, orvise versa, will cause less heat and excess exhaust. Moreover, variousambient conditions such as altitudes in different parts of the world,are variable factors that can contribute to combustion efficiency. Thecomponents of conventional gas heating appliances are generally fixedand not self-adjusting to account for these various ambient conditions.

Those skilled in the art have recognized a significant need for avariety of control systems that improved the efficiency of the fuelcombustion of gas appliances.

U.S. Pat. No. 6,398,118 issued to Rosen, et al., discloses a system formonitoring and modifying the quality and temperature of air within aconditioned space including a blower unit, a damper unit for selectivelyadmitting outside air into the conditioned space, a temperaturemoderating unit and a control unit.

The Rosen system relates to the art of conditioning indoor living andworking and other enclosed public spaces. More particularly, the patentdiscloses a system in which the carbon dioxide (CO₂) level is monitoredand controlled by apparatus in which the CO₂ sensor and supportcircuitry is integral with a thermostat which also serves toconventionally control the temperature range within the conditionedspace.

The principle of operation of the CO₂ sensor is stated to be that, thecell constituting the cathode, anode and solid electrolyte, becomessusceptible to readily measurable change in accordance with the CO₂concentration at the cell. This known effect appears to be due to achemical reaction between the CO₂ and the electrolyte which must beselected to enhance the extent of the change in accordance with the gasof interest. Combinations of electrodes and electrolytes suitable forthe purpose are discussed, for example, by S. Azad, S. A. Akbar, S. G.Mhaisalkar, L. D. Birkefeld and K. S. Goto in the Journal of theElectrochemical Society, 139, 3690 (1992). One suitable combinationwhich gives very good results for measuring CO₂ concentration is:platinum (Pt) for the cathode, reference electrode 30; silver (Ag) forthe anode, sensing electrode 31; and a mixture of Na₂ CO₃, BaCO₃ and AG₂SO₄ as the solid electrolyte.

U.S. Pat. No. 6,286,482 issued to Flynn, et al., discloses a premixedcharge compression ignition engine, and a control system, whicheffectively initiates combustion by compression ignition and maintainsstable combustion while achieving extremely low oxides of nitrogenemissions, good overall efficiency and acceptable combustion noise andcylinder pressures. The Flynn engine and control system effectivelycontrols the combustion history, that is, the time at which combustionoccurs, the rate of combustion, the duration of combustion and/or thecompleteness of combustion, by controlling the operation of certaincontrol variables providing temperature control, pressure control,control of the mixture's autoignition properties and equivalence rationcontrol. The combustion control system provides active feedback controlof the combustion event and includes a sensor, e.g. pressure sensor, fordetecting an engine operating condition indicative of the combustionhistory, e.g. the start of combustion, and generating an associatedengine operating condition signal. A processor receives the signal andgenerates control signals based on the engine operating condition signalfor controlling various engine components to control the temperature,pressure, equivalence ration and backlash or autoignition properties soas to variably control the combustion history of future combustionevents to achieve stable, low emission combustion in each cylinder andcombustion balancing between the cylinders.

The Flynn patent discloses a strategy for controlling the start anddirection of combustion by varying the air/fuel mixture autoignitionproperties. The autoignition properties of the air/fuel mixture may becontrolled by injecting gas, e.g. air, oxygen, nitrogen, ozone, carbondioxide, exhaust gas, etc., into the air or air/fuel mixture either inthe intake system.

U.S. Pat. No. 6,392,536 issued to Tice, et al. discloses amulti-function detector which has at least two different sensors coupledto a control circuit. In a normal operating mode the control circuit,which would include a programmed processor, processes outputs from bothsensors to evaluate if a predetermined condition is present in theenvironment adjacent to the detector. In this mode the detector exhibitsa predetermined sensitivity. In response to a failure of one of thesensors, the control circuit processes the output of the remainingoperational sensor or sensors so that the detector will continue toevaluate the condition of the environment with substantially the samesensitivity.

U.S. Pat. No. 5,644,068 issued to Okamoto, et al. discloses a gas sensorof the thermal conductivity type suitable for the quantitative analysisof the fuel vapor content of a fuel-air mixture. The Okamoto gas sensorcomprises a sensing element and a compensating element, each of whichincludes an electrically-heated hot member incorporated into aWheatstone bridge circuit powered by a constant current supply circuit.The constant current supply circuit is adjusted and regulated such thatthe hot member of the sensing element is heated with an electric currentof such an intensity that corresponds to a point of transition (Y) atwhich, at the interface of the hot member and the mixture, thepredominant mode of heat transfer changes from thermal conduction tonatural convection.

The disclosures of the foregoing patents are hereby incorporated by thisreference.

While recognizing the advantages of control systems utilizing exhaustgases as possible parameters to improve efficiency, these systems do notprovide the critical recognition of exhaust gas concentration levels,such as carbon dioxide, for continuous active feedback control of futurecombustion events. The present invention achieves these goals.

SUMMARY OF THE INVENTION

A unique control system is provided for optimizing and for effectingefficient combustion of gas appliances by controlling the proportion offuel and air variables. The combustion control system providescontinuous active feedback control of the combustion event by detectingthe level of exhaust gases such as CO₂ within a prescribed optimumrange. The system comprises a qualitative and quantitative sensor andprocessor to trigger the modulation of a valve to adjust pressure andgas flow to combustion chamber of gas appliance, when the concentrationof the detected gas falls outside the prescribed optimum range.Accordingly, the control signal varies the proportion of air to fuelinflow to a prescribed optimum range for future events thereby achievingefficient fuel combustion.

The present invention achieves improved combustion efficiency byadjustment of pressure and fuel flow related to changing ambientconditions. In a presently preferred embodiment, the inventive systemcomprises a CO₂ sensor to continuously measure the concentration levelof carbon dioxide of the combustion chamber. The sensor generates asignal, including detected qualitative and quantitative measurements,that is received by a microprocessor. The processor, in turn, comparesthe received sensor signal with prescribed levels, and determineswhether to adjust a pressure regulator of a gas valve to bring theair/fuel mixture to a prescribed optimum range for future combustionevents.

In one embodied form, the system comprises active feedback control meansbased upon detection of the concentration of carbon dioxide. Assumingfixed exhaust gas flow from combustion, the prescribed concentrationlevel of carbon dioxide gas for optimum efficiency is within a range ofabout seven and one half percent (7.5%) to about eight percent (8%).Accordingly, if for example, the sensor detects a concentration level ofnine percent (9%) carbon dioxide, the control means will accordinglydecrease the air flow into the burner of the gas appliance. If theconcentration of carbon dioxide in the exhaust gas is less than sevenpercent (7%), the control means will proportionately increase the intakeair flow to the combustion chamber. Thus greatest combustion efficiencycan be achieved by monitoring and maintaining the concentration ofcarbon dioxide within the prescribed range.

In a second embodiment, the inventive system comprises a CO₂ sensor, COsensor, O₂ sensor to trigger the modulation of gas valve to adjustpressure of gas pressure and gas flow to combustion chamber of gasappliance. In operation, modulation will take place, should the detectedcarbon dioxide concentrate within the gas mixture falls outside aspecified range of concentration. Modulation of the inventive gas valvecan be to such an extent to minimize gas flow to future combustionevents.

The inventive system comprises a processor that receives the qualitativeand quantitative signal from the carbon dioxide sensor and providesfeedback control to an electronic control unit (ECU). ECU receives thesensor signal and processes the signal to determine the appropriateadjustment, if any, to the flow of air to be mixed with fuel forcombustion in the burner unit. The signal reflecting the carbon dioxideconcentration in the exhaust gas is then compared to a predetermineddatabase of desired airflow adjustment values. Based on the comparisonof the actual airflow to the desired airflow adjustment value, the ECUthen generates a plurality of output signals, for variably controlling apressure regulator of a gas intake flow valve and other respectivecomponents of the system so as to effectively ensure, that the futurecarbon dioxide concentration in the exhaust gas is maintained within theprescribed optimum range.

The combustion control scheme is most preferably implemented in softwarecontained in ECU that includes a central processing unit such as amicro-controller, micro-processor, or other suitable micro-computingunit. Accordingly, the unique system achieves high efficiency combustionin a wide variety of gas heating appliances.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional side view of one embodied CO₂ sensor andPitot tube in accordance with the present invention.

FIG. 2 is a side sectional view illustrating the system components andplacement of a CO₂ sensor in the control processor in accordance withthe present invention.

FIG. 3 is a schematic sectional view depicting a gas valve in accordancewith one embodied form of the invention.

FIG. 4 is a schematic flow chart indicating the components andinteraction of the high efficiency fuel injection system for gasappliances in accordance with the present invention;

FIG. 5 is a schematic flow diagram of one embodied form of the inventivesystem and further indicating the levels of CO₂ detected to activate themodulation of the inventive gas valve to adjust pressure and flow of gasto the combustion chamber in accordance with one embodied form of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A unique control system is provided for gas appliances to achieveefficient combustion by controlling the proportion of fuel and airvariables. The combustion control system provides active feedbackcontrol of the combustion event and includes a CO₂ to trigger themodulation of a gas valve to adjust pressure of gas pressure and gasflow to combustion chamber of gas appliance. Detection of othercombustion gases such as carbon monoxide and oxygen may also be utilizedby the system, with carbon dioxide gas being the principal gas fortriggering the modulation of the gas valve. A microprocessor receivesthe concentration signals from the sensors and generates control signalsbased on the concentration signal for controlling a pressure regulatorof the gas valve so as to variably control future combustion events toachieve maximum fuel combustion efficiency. Accordingly, the controlsignal varies the proportion of air to fuel inflow to a prescribedoptimum range achieving efficient fuel combustion.

In a presently preferred embodiment, the present invention provides animproved method and apparatus for achieving high efficiency ofcombustion by comprising active feedback control means based upondetection of the concentration of carbon dioxide within the prescribedoptimum range of about 7.5% to about 8.0%. Assuming fixed exhaust gasflow from combustion, if the concentration level of carbon dioxideexceeds about nine percent (9%), the control means will accordinglydecrease the air flow into the burner of the gas heating appliance. Ifthe concentration of carbon dioxide in the exhaust gas is less thanseven percent (7%), the control means will proportionately increase theintake air flow to the combustion chamber. Thus greatest combustionefficiency can be achieved by monitoring and maintaining theconcentration of carbon dioxide within the prescribed range.

In a second embodiment, the inventive system comprises a CO₂ sensor, COsensor, and O₂ sensor to trigger the modulation of gas valve to adjustpressure of gas pressure and gas flow to combustion chamber of gasappliance. In operation, modulation will take place if the CO₂ contentof the gaseous mixture falls outside the prescribed range ofconcentration. For instance, in the case of CO₂, modulation is withinthe range of 7 percent to 9 percent. Gas pressure and flow will beadjusted in responding to changes of concentration, before CO₂ reaches 7percent or 9 percent. Actually, modulation of gas value can be to suchan extent to minimize gas flow.

The sensor module provides a O-4VDC output scaled to 0-2000 ppm CO₂. Thesampling method for detection of the carbon dioxide concentration may beeither flow through or diffusion and can be configured to measure ppmlevels up to 5%. The modules include self-calibration algorithm thateliminates the need for on-going calibrations.

The CO sensor is operational to trigger the modulation of gas valve tolower the amount of gas flow to combustion chamber of gas appliance. Ifthe concentration is less than 65 PPM, the sensor is not activated.Preferably, the CO sensor accumulates concentration up to 65 PPM ofcarbon monoxide in one hour.

The O₂ sensor is operational to trigger the modulation of gas valve tolower the amount of gas flow to combustion chamber of gas appliance. Ifthe level is over 19.5 percent, the sensor is not activated.

The system may use conventional shut off mechanisms for instancedisclosed in U.S. Pat. No. 5,838,243, which is hereby incorporated bythis reference.

After generating the sensor concentration signal, the control processorwill determine the desired adjustment of air inflow by setting thepressure regulator of a gas valve to a prescribed optimum range.

The modulating gas valve will preferably comply with applicable industryand governmental standards. e.g. AGA Requirements for automatic,non-shutoff modulating gas valves No. 1-92 (1992) which is herebyincorporated by this reference.

This standard applies to produced automatic modulating valves, hereinafter referred to as valves, hereinafter referred to as valves, and thevalve control system, constructed entirely of new, unused parts andmaterials. These valves may be individual valves, valves utilized asparts of automatic gas ignition systems, or the modulating valvefunctions of combination controls.

These valves are intended to be used to vary the gas input rate to theappliance, as a function of the signal from the gas valve controlsystem. These valves are not intended to provide for complete shutoff ofthe gas flow to the main burners.

Those skilled in the art will recognize that the inventive system iscapable of activation and modulation by detection of carbon dioxidelevels, within a prescribed range of from about 6% to about 10%.

The following summary provides the modulation parameters to improvecombustion efficiencies:

Activation:

-   -   Range of sensor between about 6% to 10% of CO₂ concentration    -   0.5% of CO₂ changes would activate gas control to modulate        outlet pressure by 0.36″ W.C. to 0.39″ W.C.    -   If 9% of CO₂ by the sensor, gas control would modulate pressure        downward to 2.87″ W.C. from 4.0″ W.C.    -   If 6.5% of CO₂ by the sensor, gas control would modulate        pressure upward to 4.25″ W.C. from 4.0″ W.C.

Typically, the mechanisms of valves will be protected by substantialenclosures so as to prevent interference with the safe operation of thedevices.

Pins, stems, or other linkage passing through the valve body or casingshall be sealed to provide gastight construction.

Diaphragm type automatic valves in which a flexible nonmetallicdiaphragm constitutes the only gas seal and which utilize control gas onthe atmospheric side of the diaphragm shall have the atmospheric side ofthe main diaphragm enclosed in a gastight casing with means provided forbleeding the control gas.

Valves in which a flexible nonmetallic diaphragm constitutes the onlygas seal shall have the atmospheric side of the diaphragm enclosed tolimit the leakage to atmosphere in the event of diaphragm rupture to notmore than 1.0 cubic foot per hour at the maximum pressure rating of thevalve when tested with a gas having a specific gravity of 1.55 or shallbe provided with means for venting the gas in the event of diaphragmrupture.

The CO₂ Sensor module communicates over an synchronous, UART interfaceat 9600 baud, no parity, 8 data bits, and 1 stop bit. When the hostcomputer of PC communicates with the sensor, the host computer sends arequest to the sensor, and the sensor returns a response. The hostcomputer acts as a master, initiating all communications, and the sensoracts as a slave, responding with a reply.

Preferably, sensor commands and replies are wrapped in a securecommunications protocol to insure the integrity and reliability of thedata exchange. One suitable communications protocol for the serialinterface and the command set for the module CO₂ Sensor are set forthbelow.

Each command to the sensor consists of a length byte, a command byte,and any additional data required by the command. Each response from thesensor consists of a length byte and the response data if any. Both thecommand to the sensor and the response from the sensor are wrapped in acommunications protocol layer.

Command: <length><command>additional_data>

Response: <length><response_data>

The communications protocol consists of two flag bytes (0xFF) and anaddress byte as a header, and a two-byte CRC as a trailer. In addition,if the byte 0xFF occurs anywhere in the message body or CRC trailer, theprotocol inserts a null (0x00) byte immediately following the 0xFF byte.The inserted 0x00 byte is for transmission purposes only, and is notincluded in the determination of the message length or the calculationof the CRC. Header Message Body Trailer <flag><flag><address><Command/Response> <crc_Isb><crc_msb>

When receiving a command or response, the flags and any inserted 0x00bytes must be stripped from the message before calculating theverification CRC. A verification CRC should be computed on all receivedmessages from the sensor and compared with the CRC in the messagetrailer. If the verification CRC matches the trailer CRC, then the datafrom the sensor was transmitted correctly with a high degree ofcertainty.

In response to the concentration signal from the sensor module the airflow from a gas valve will be adjusted by pressure regulator before itflows to burner, prior to combustion chamber. If concentration of carbondioxide is more than 9 percent (9%), gas flow will be adjusted upward toincrease its mixture with air; and if concentration of carbon dioxide isless than 7 percent (7%), gas flow will be adjusted downward to decreaseits mixture with air.

FIG. 4 is a schematic flow chart indicating the components andinteraction of the high efficiency fuel injection system for gasappliances in accordance with the present invention;

FIG. 5 is a schematic flow diagram of the inventive system and furtherindicating the levels of CO₂ detected to activate the modulation of theinventive gas valve to adjust pressure and flow of gas to the combustionchamber in accordance with one embodied form of the present invention.

In the CO₂ module, a bus interfaces to both an external processor andthe A/D converter which is collecting the CO₂ data. When the module iscollecting data, its serial shift clock is configured to generate itsown internal clock. That is, the module is said to be operating in“master” mode. When the CO₂ module is communicating with an externalprocessor, it relies upon the external processor to supply the clockpulse, called the “slave” mode.

Thus, to an external process, the CO₂ module appears as a slave on thebus. The external processor is the master, meaning that it provides theSK clock signal for both sending and receiving data across the bus. Fromthe CO₂ module's point of view, during communications with an externalprocessor, is SI (serial in) and SK (serial clock) are inputs, and itsSO (serial out) is an output. Additionally, there are two digitalhandshake lines that an external processor uses to communicate with theCO₂ module.

Every data exchange between an external processor and the CO₂ modulestarts with the external processor sending a request data-packet—severalbytes—to the CO₂ module. The CO₂ module then responds by returning aresponse data-packet to the external processor. The request data packetcontains a command byte, and perhaps one or more parameter bytes.

After receiving each byte in a request data packet, the CO₂ moduleraises the UB_ACK handshaking line. When it is ready to receive the nextbyte it lowers UB_ACK. The external processor must send the next byte tothe CO₂ module within 10 milliseconds from the time the UB_ACK line goeslow. This handshaking between bytes provides flow control and insuresthat the external processor does not overrun the CO₂ module's inputbuffer and that the CO₂ module does not wait indefinitely for theexternal processor to send the next byte. After receiving the final byteof the request data-packet, the CO₂ module again raises UB_ACK.

When the CO₂ module has processed the request and is ready to send thefirst byte of the response data-packet, the CO₂ module lowers UB_ACK.The external processor has 10 milliseconds from the time the UB_ACKlines goes low in order to start the clock and receive the byte. Aftertransmitting the byte, the CO₂ module raises UB_ACK, and lowers it againwhen it is ready to transmit the next byte. The process continues untilall bytes of the response data-packet have been transmitted to theexternal processor. The 10 millisecond time limit insures that the CO₂module does not wait indefinitely for the external processor to startthe clock to receive the byte.

After sending the final byte in a response, the CO₂ module raises UB_ACKand leave it high. The external processor then raises UB_REQ, concludingthe data interchange. UB_REQ must stay high longer than a specifiedminimum before the external processor lowers it to start the next dataexchange.

At the conclusion of a response data packet, the CO₂ module will waitapproximately 100 milliseconds after the final UB_ACK goes high beforeinitiating its return to master mode and the resuming of datacollection. If the external processor raises and lowers UB_REQ duringthis delay interval, the module stays in slave mode and immediatelyservices the new request. The delay interval gives the externalprocessor the opportunity to send a series of commands in rapidsuccession to the module. Note that the CO₂ module is not functioning asa sensor while it is in the slave mode.

The raising of UB_REQ, together with the expiration of the delay timeinterval, is the signal to the CO₂ module to return to Microwire mastermode and resume its A/D converter data collection. Microwire modeconversion and re-initialization for data collection is a time consumingprocess, and the module has only three opportunities during the processto abort and respond to a new UB_REQ. Hence, for non-PPM/Temperaturerequest, it is most time-efficient to start the next UB-REQ during thedelay interval following the previous request.

If the external processor needs to terminate an incomplete data exchangeit raises the UB_REQ line. When the CO₂ module see this, it discards thecontents of its communication buffers and then respond by raising theUB_ACK.

If the CO₂ module needs to terminate an incomplete data exchange, itraise UB_ACK. If UB_ACK remains high longer than the maximum timespecified for UB_ACK High Between Bytes, then the external processormust recognize this as termination of an incomplete data exchange. Forexample, if the CO₂ module receives bytes that do not correspond to avalid request data-packet then it raises UB_ACK and holds it high,signaling termination of an incomplete data exchange.

The CO₂ module starts a 10 millisecond timeout timer each time it lowersUB_ACK. The external processor must respond by starting the serial shiftclock within this interval so that the module can transmit or receivethe pending byte. If the external processor fails to start the clock,the CO₂ module presumes that the communication has been aborted and willraise UB_ACK.

If either the external processor or the CO₂ module terminates a dataexchange, no new communication can be initiated until both UB_ACK andUB_REQ have return to the high state. The new command then starts withthe external processor lowering UB_REQ as described above.

The inventive system comprises a processor that receives the qualitativeand quantitative signal from the carbon dioxide sensor and providesfeedback control to an electronic control unit (ECU). ECU receives thesensor signal and processes the signal to determine the appropriateadjustment, if any, to the flow of air to be mixed with fuel forcombustion in the burner unit. The signal reflecting the carbon dioxideconcentration in the exhaust gas is then compared to a predetermineddatabase of desired airflow adjustment values. Based on the comparisonof the actual airflow to the desired airflow adjustment value, the ECUthen generates a plurality of output signals, for variably controlling apressure regulator of a gas intake flow valve and other respectivecomponents of the system so as to effectively ensure, that the futurecarbon dioxide concentration in the exhaust gas is maintained within theprescribed optimum range.

The combustion control scheme is most preferably implemented in softwarecontained in ECU that includes a central processing unit such as amicro-controller, micro-processor, or other suitable micro-computingunit. Accordingly, the unique system achieves high efficiency combustionin a wide variety of gas heating appliances.

The following example provides the presently preferred parameters forachieving high efficiency combustion:

EXAMPLE

General

-   -   02 reaches 18.2%, CO is present dangerous level of 80PPM per        hour. In testing, 18% of O2, CO detector still shows 43PPM per        hour.    -   Accuracy of CO sensor alone, without Co₂ sensor) cannot be        counted for real application.    -   Monitoring CO2 concentration is preferred to measure and monitor        for combustion efficiency of a gas heating appliance.        Function Required for Gas Control    -   Range of Regulation: minimum 20,000 BTU per hour, maximum        200,000 BTU per hour    -   Operating Inlet pressure: max. ½ PSI, Natural gas 7.0″ w.c., LP        11.0″ W.C.    -   Range of Modulation: Natural gas 1.7″-4″ w.c. +/−0.3″ w.c., LP        5″-10″ w.c. +/−0.5″ w.c.        Mechanical Requirement for Gas Control:    -   ½″ or ¾″ Inlet and Outlet        Electrical Requirement    -   Gas Control: 24 VAC    -   Sensor: 5 VDC, Analog output: 0-4 VDC    -   Modulation: 5 VDC        Configuration: Furnace T1. Sampling System T2, Sensor T3    -   Copper Tubing needs to be short to minimize differential of T1        and T2, dia. of 0.25″ to 0.5″    -   Copper Tubing in vertical coil to cool the flue down to 140        degrees F. and remove condensation    -   At 1 cc/min. flow rate of CO2 sapling from T1, through T2, to T3        Operation Requirement    -   Preferred range of CO₂ concentration for optimum combustion        efficiency is about 7.5% to 8.0%    -   If 9% of CO2, outlet gas pressure should be modulated downward        from 4.0″ to 2.97″    -   If 6.5%, outlet gas pressure should be modulated upward from        4.0″ to 4.5″ w.c.    -   If 9.5%, outlet gas pressure should be modulated downward by 1″        w.c.    -   A 0.5% change of CO2 would result in a modulation of outlet        pressure by 0.36-0.39″ w.c.        Sensor    -   Power consumption: 150 mA peak, 30 mA average. Power supply        5VDC+/−5%    -   Range of measuring: 7% to 11%, accuracy +/−5% of reading    -   Gravity flow rate of CO2 is 1 cc per minute    -   Operational temperature is 10 to 185 degrees F., relative        humidity 0 to 100%, non-condensing    -   Warm Up Time: 20 minutes    -   Response Time: TBD as it is up to length of tubing, its area,        and flow rate of 1 cc/minute    -   Step Response Time (to 90% of the step—5 minutes

1. A control system for optimizing and for effecting efficientcombustion of fuel by a gas appliance, the system comprising incombination: a) means for qualitative and quantitative determination ofcombustion exhaust gas from the gas appliance; b) sensor means fordetecting the concentration of carbon dioxide present in the combustionexhaust gas; c) means converting the detected concentration of carbondioxide to a digital detected value signal for relay to a centralprocessor unit; d) means for comparing the digital detected value signalwith a prescribed range of optimum concentration values of carbondioxide; e) means for calculating a correction factor to detected valuesignal within the prescribed range of optimum concentration values; andconverting the detected value signal to a prescribed value signal; andf) means for directing the signal derived from step e) to a regulatorvalve for adjusting the concentration of fuel and air mixture for futurecombustion events.
 2. The control system for optimizing and foreffecting efficient combustion as defined in claim 1, wherein theprescribed range of optimum concentration values of carbon dioxide isfrom about 6% to about 10%.
 3. The control system for optimizing and foreffecting efficient combustion as defined in claim 1, wherein theprescribed range of optimum concentration values of carbon dioxide isfrom about 7.5% to about 8.0%.
 4. The control system for optimizing andfor effecting efficient combustion as defined in claim 1, wherein thesensor means for detecting the concentration of carbon dioxide alsocomprises sensor means for detecting the concentration of carbonmonoxide present in the combustion exhaust gas.
 5. The control systemfor optimizing and for effecting efficient combustion as defined inclaim 1, wherein the sensor means for detecting the concentration ofcarbon dioxide also comprises sensor means for detecting theconcentration of oxygen present in the combustion exhaust gas.
 6. Thecontrol system for optimizing and for effecting efficient combustion asdefined in claim 1, wherein said means for comparing the digitaldetected value signal with a prescribed range of optimum concentrationvalues performs the comparison intermittently over time.
 7. The controlsystem for optimizing and for effecting efficient combustion as definedin claim 1, wherein said means for comparing the digital detected valuesignal with a prescribed range of optimum concentration values performsthe comparison on an continuous basis.